Conventionally, an art described in the Patent Literature 1 is known as an art of a belt-type stepless transmission in which a belt is wound round a pair of pulleys whose widths of grooves are variable so as to transmit power.
The belt-type stepless transmission described in the Patent Literature 1 has a cam mechanism which controls a pressing power of pulley on a belt corresponding to a transmitted torque. The cam mechanism includes a pair of cams fixed respectively to a movable sheave and a transmission shaft which are provided in the pulley, a cam roller arranged between the cams so as to touch the cams always, and an elastic member applying power on the cams so as to rotate the cams along a predetermined direction. In this construction, a torque transmitted from the pulley is transmitted via the cam roller to a power transmission shaft. By the cams and the cam roller, the pressing power of the pulley on the belt can be controlled corresponding to the transmitted torque.
However, the belt-type stepless transmission described in the Patent Literature 1 requires members such as the pair of the cams, the cam roller and the elastic member, thereby being disadvantageous because the structure is complicated and the production cost and the part cost are high.